Bristlecones and Sagebrush

In MM05 (EE), we reviewed literature on bristlecones because these trees were supposed to be unique radio receivers for world temperature. Obviously the specialist literature stood against this proposition. We cited a number of interesting articles by Mooney in American Midland Naturalist in the 1960s – none of which are considered by Juckes in his “evaluation” of millennial reconstructions, including the following:

Even in higher stands, their [bristlecone] principal botanical competition in many locations is with big sagebrush [Wright and Mooney, 1965; Mooney et al., 1964] with bristlecones outcompeting big sagebrush on moister dolomite substrate. This effect is vividly illustrated by Figure 2 of Wright and Mooney [1965], where the sharp geological contact between the dolomite and sandstone is clearly shown by the change from bristlecone pines to sagebrush at the same elevation The same effect is also perhaps shown in the charming 19th century painting (Figure 7), where a sharp change in vegetation at the same elevation is easily observed.

Here is the very interesting Figure 2 from Wright and Mooney [1965]. I’m probably more used to looking for geological contacts than most of you, but there is a really remarkable vegetation demarcation of the contact between granite and dolomite illustrated in the picture below. What makes this particular picture so remarkable is that the contact is marked by a vegetation contrast – bristlecones on the dolomite; sagebrush on the granite or sandstone. Since the geological contact runs uphill-downhill, the contrast is clearly differentiated from an altitudinal gradient usually associated with temperature.
At the NOAA website on drought, the following 19th century water color is shown (illustrated in MM05 (EE)). Although there is no specific statement that this water color illustrates a similar geological contact, there is a very similar-looking vegetation contact running uphill-downhill, which I suspect is due to the same phenomenon.

Here are some comments from Wright and Mooney 1965:

The main objective of this study was to determine the environmental gradient or complex of gradients that controls the distribution of bristlecone pine on the White Mts. However it soon became apparent that any consideration of bristlecone pine distribution must include a study of sagebrush since their patterns are complementary…

Sagebrush accounts for only 13% of the shrub cover on dolomite but on sandstone it constitutes 75% and on granite 78% of the total shrub cover. Sagebrush is comparatively least abundant on dolomite. This face alone acconts for a substantial difference in total shrub cover among the three substrates, since cover by other shrubs is low on all three….

A comparison between treatments for any given soil indicates that all soils are severely deficient in phosphorus, but the deficiency is most severe on dolomite…

It appears then, in answer to the question posed earlier, that bristlecone pine is responding in gross terms primarily to a moisture gradient in the White Mts. This would explain how its distribution runs counter to most of the subalpine herb and shrub components which seem to be controlled essentially by temperature gradients. This viewpoint is an obvious simplification of the complex environmental relationships operative in controlling plant distribution in the subalpine zone of the White Mts. However most of the mechanisms which have been described tht favor the development of bristlecone over sagebrush, its most severe competitor, can be explained directly or indirectly on a basis of moisture balance.

It seems pretty obvious to me that any species that is competing with sagebrush is moisture-limited and that there will be, at a minimum, an interaction effect between temperature and precipitation. Juckes’ current line of justification is to issue the curious challenge for us to show that bristlecones are a worse temperature proxy than the other so-called “proxies”. No, Martin, the challenge is for proponents of bristlecones/foxtails to show that they are valid temperature proxies. There were plenty of warnings in the literature prior to MBH98. There are more warnings now.

42 Comments

Spent a bit of time in the Whites and nearby environs doing geophysical field work. There has never been a question in my mind that BCPs are moisture limited. The area in question is a classic example of a place which couldn’t make up its mind whether it wanted to be alpine or high desert. In this case, the substrate is a deciding factor – given the general lack of moisture, the less retentive substrate cannot support BCPs, only sage brush.

However most of the mechanisms which have been described tht favor the development of bristlecone over sagebrush, its most severe competitor, can be explained directly or indirectly on a basis of moisture balance.

Can’t remember where I found the article, but some Forest Service guys attribute the increased growth in bristlecones in this area to more/later snowpack.

In my experience working with paleo-climatologists 25 years ago, I found most came from geological backgrounds and training and had little interest in the biology of the organisms that provided proxy records. Maybe it was because sediments only slowly respond to environmental changes and bioturbation mixes many years of accumulation that they didn’t really consider it important. This blind spot is a huge flaw in the logic of proxy studies. When it comes to tree cores, even though they originally may have been taken by botanists, the uses to which they are put in climatological studies largely seems to ignore the individuality of specimens and the influence of micro-environments. This source of error right at the beginning adds unknowable uncertainty to the statistical uncertainty and should make any conclusions suspect at the very least. It strongly argues for multi-disciplinary studies that include biologists, statisticians, physicists, meteorologists, etc.

Here is a literature review of studies on factors affecting growth rates of subalpine conifers (Steve has probably cited this somewhere). It includes the following statement:

As noted previously, there are several potential explanations for recent increased growth in subalpine conifers. The possibility of carbon dioxide fertilization has been supported by experimental studies (Graybill and Idso 1993), but is extremely difficult to demonstrate for mature trees in the field. Increased temperature is another potential cause, but its relationship with growth is correlative and also difficult to demonstrate for mature trees. Changes in snowpack duration, which affects length of growing season, are a more likely cause of growth increases. Unfortunately, the long-term relationship of snowpack to tree growth has not been adequately investigated because snowpack data are often difficult to obtain.

Hockey Team rules would indicate that, while evidence against the BCP exhibiting a measurable temperature signal can be presented, only a direct proof that they have no signal would make them conditionally subject to removal for proxy consideration. That condition would be that they perform worse than other proxies. If those other proxies are shown to have little or no temperature signal would that put the BCPs back in play or would that portend restarting tree ring proxy reconstructions from scratch? Remember this is the Hockey Team and you play by their rules.

If BCP tree ring responses are moisture limited that might shift their response from local temperatures to more distant and temporally extended regional temperatures that influence precipitation — warmer equals wetter and colder equals drier. Would that qualify me to tend goal for the Hockey Team?

Yabut, analyzing a precip indicator to infer temperature is unconsciounable! You would no doubt be banned from ever publishing in scientific journals and also summoned before Congress to answer for your crimes. Unless of course the precip indicates a warming trend…;-)
Earle

Even Mann states in MBH98 that lacking proof of a linear relationship between temperature
and ring width, the proxies cannot be trusted. He then continues on, to this day apparently,
to use this hypothesis as “truth,” in spite of never offering such proof.

That’s how science works, right? State your hypothesis, then test it, then verify/falsify
it, before using it for further hypotheses (or removing it due to lack of validity). Why
is this concept so hard for climatologists to understand?

That’s how science works, right? State your hypothesis, then test it, then verify/falsify
it, before using it for further hypotheses (or removing it due to lack of validity). Why
is this concept so hard for climatologists to understand?

Because the Hockey Team are not being paid to be transparent, logical or rational – just consistent.

Even Mann states in MBH98 that lacking proof of a linear relationship between temperature and ring width, the proxies cannot be trusted.

But their negation of linear is highly nonlinear. Assumptions of MBH98.. You gotta love them

Implicit in our approach are at least three fundamental assumptions.. The indicators in our multiproxy trainee network are linearly related to one or more of the instrumental training patterns. In the relatively unlikely event that a proxy indicator represents a truly local climate phenomenon which is uncorrelated with larger-scale climate variations, or represents a highly nonlinear response to climate variations, this assumption will not be satisfied.

For the time being, we circumvent this problem by restricting the calibration of the density data to the period before 1960.. This situation is far from ideal, but the alternative … would invariability produce earlier estimates of past temperature that, to some extent, too warm.

In the absence of a substantiated explanation for the decline, we make the assumption that it is likely to be a response to some kind of recent anthropogenic forcing. On the basis of this assumption, the pre-twentieth century part of the reconstructions can be considered to be free from similar events and thus accurately represent past temperature variability. [Briffa et al. 2002]

In the relatively unlikely event that a proxy indicator represents a truly local climate phenomenon which is uncorrelated with larger-scale climate variations, or represents a highly nonlinear response to climate variations, this assumption will not be satisfied.

So, if tree rings, or ANY OTHER PROXY, reflects only LOCAL temperatures, which they HAVE to do, if they are legitimate proxies, then the assumption is not satisfied. Talk about ridiculous reasoning. Maybe I’m missing something, but this does not make any sense to me.

#15, Wait a second. I thought thought that it had been discussed that the proxies did not necessarily reflect local temperatures,
but instead mapped to global temperatures at disparate places based on “tele-connections” :). Maybe it’s just the butterfly effect
in action. A butterfly beats its wings in India and bcp’s in North America show a temperature increase.

So, if tree rings, or ANY OTHER PROXY, reflects only LOCAL temperatures, which they HAVE to do, if they are legitimate proxies, then the assumption is not satisfied.

I think that is not what they mean, but I’m unable to decode the sentence accurately (me non-native speaker (NNS)). proxy indicator represents a truly local climate phenomenon which is uncorrelated with larger-scale climate variations or something.. But anyway, IMO any local climate phenomenon cannot be uncorrelated with climate.

#14

LOL. Can’t believe it. Googled it, found your NAS ppt. Page 10. Why don’t you apply CVM for the top figure? Why they choose lots of proxies for INVR but small amount for CVM? Is this over soon? :)

Steve, page 41 in your NAS ppt predicts CVM: ‘Variance is already rescaled’. Multivariate calibration and CVM after that, overfitters dream. (and in general, the presentation is very impressive, first time I saw it! ). Now, just take those 450 series and apply Juckes et al A2 procedure.

Could changes in rainfall pH also cause changes in nutrient availability? I suppose what I am getting at here is that there are so many different signals that could be present in a plant growing at the edge of existence that any small change could make a big difference. It might be difficult to sort out rainfall from temperature from pH from CO2 from nutrients available in soil from a dead elk carcass nearby, etc. I don’t doubt that bristlecone pines are a proxy but they are probably a combined proxy for many different things at the same time. An organism living in a harsh environment could exhibit a dramatic change itself in the face of a small change in any one of many different environmental conditions.

Might be interesting to see the differentials of the bristlecones when compared to rainfall instead of temperature. Bet it matches up as well or possibly better than temperature.

Oh yes, nobody. These and other ideas have been discussed at length. Tree rings are,
apparently, a non-linear function of a variety of forcers, temperature, CO2 fertilization,
soil ph, etc., included. The common HT claim, however, is that they have chosen only
those trees that are sensitive to temperature (i.e. not sensitive to rainfall) and the
resulting correlation (which is not all that great, and abysmal in some instances) MUST
therefore be from temperature. Yes, the argument is also circular.

20, 21: It has been my contention since I started posting on this blog about 1-1/2 years ago that it is not feasible to use tree rings as a temperature proxy, given the present knowledge. I think the folks here are validating this viewpoint.

I suppose it would be feasible to use tree rings but I would want to use rings from an area where temperature is the primary constraint on growth and other conditions for growth were in enough abundance that a minor variation wouldn’t amount to much. Bristlecone pines tend to grow where almost all resources needed for growth are sparse and a change in any of them would be noticed.

In other words, I would want to sample where I would think temperature would be the dominant signal, not where the signal would be expected to be very noisy. A place where there was more than enough rainfall but short gowing seasons, for example, would be my preference if I wanted a temperature guage.

Nobody: that’s what they all claim to be doing. Trouble is finding places like that. You have to go near treeline, and most treeline locations have the same problems as with the bristlecones. There are probably some locations that meet your criteria, but I think they are very rare. I saw one study done in Idaho that looked promising, but there are still a lot of possible unknown influences, especially when you get back hundreds of years. There are much better proxies out there than tree rings, IMO.

#26. The Idsos used extensive direct quotations denoted by actual quotation marks. Many civilians would think that this would make it almost impossible for distortion to occur, but this is simplistic. A proper Team summary requires paraphrasing. (I don’t think any Team account of MM has ever included a direct quotation.)

By failing to paraphrase and reliance on direct quotations, the Idsos have, by definition, introduced a “distortion” from how the Team summary would have appeared.

Did my undergraduate field camp in the southern white mountains just east of Lone Pine. Bender, Go to the old Cerro Gordo Gold Mine for some good info. Plus the exposures are all around the area. As I recall it was like Ordivician age slate on top of younger sandstones and an extreme amount of limestone /dolomite. The Bristlecone pines were on top, rooted in the Slates, not in the limestone. I believe the youngest units were like Triassic or something. It was 10 years ago, sorry for not being more sure.

On the other hand. I have a copy in my garage of the official USGS mapping of the entire area. Its from like 2004, 2005. Post if you really want a copy and I can make one available. I never thought that desolite area would ever become so popular.

#28. I wouldn’t place much weight on this particular recollection as the mapping of bristlecones on dolomites is firm (and the first mapping was done by geologists). Bristlecones also occur on sandstones, but the dolomite substrate is important and distinct.

In the relatively unlikely event that a proxy indicator represents a truly local climate phenomenon which is uncorrelated with larger-scale climate variations, or represents a highly nonlinear response to climate variations, this assumption will not be satisfied.

Let’s say the proxy indicator is a fluid in a glass tube detecting a local change in the heat transfer characteristics in an urban area. What then?

The Idsos used extensive direct quotations denoted by actual quotation marks. Many civilians would think that this would make it almost impossible for distortion to occur, but this is simplistic.

I agree, but I still have not seen an example of them mischaracterizing a study. Of course, they do add interpretations, which are not in the study (Lee’s problem). But they certainly have the right to do that.

I was trying to be ironic. I am really tired of Team paraphrasing. I try to use direct quotations as much as possible and I would like to see the Team try using direct quotations – instead of putting words in other people’s mouths.

A place where there was more than enough rainfall but short gowing seasons, for example, would be my preference if I wanted a temperature guage.

The problem with a short growing season then, is what exactly are you measuring w.r.t. temperature? I.e.,
the proxy is then only indicative of the growing season temps, not the whole year. This is another point
never mentioned when using proxies. A year could easily have a warm summer followed by an unusually cold
winter, but the ring-growth would, presumably, only indicate the growing season, which is in the summer.

I’m still relatively early-on into all of this gw stuff, but when I first heard about Bristlecone Pine tree rings as proxies for temperatures I struggled to cry out desperately, “But, but – each individual tree is different”, not having to wait for Tom Cruise to help me commit suicide to realize it. [The Last Samurai]

Likewise, I’ve lived for 30 years in mountain forest and high desert and think so far that using tree rings as a proxy for temperatures is very dubious. Just anecdotally, I’ve noticed that older dead Lodgepole Pine trees I’ve cut down for firewood have much narrower rings towards the later part and end of their lives. The last one another guy cut down for me this year was a 2 foot diameter tree which died about 5 years ago. It turned out to be about 100 years old, but I really couldn’t accurately count the last ~ 10 rings by eyeballing them, and the previous x number or them were shrinking. It hasn’t been getting that cold around here.

I have a hard time imagining that Bristlecones wouldn’t do the same kind of thing – as they “age”? But I don’t know anything about them from personal experience.

Anyway, I maintain that each individual tree is different according to how it can compete with everything in its immediate locale in order to survive, given also its own genetics, perhaps making the selection of individual trees as proxies for anything other than general conditions within small areas difficult. Water availability is obviously a big factor among general conditions necessary for tree growth, but maybe rings don’t necessarily reflect it either in a direct way compared to all other factors.

38: It is normal for ring widths to get more narrow as the tree ages, even if conditions are constant. I agree with most of your views on using rings as a proxy. Too many uncertainities to allow much confidence in them.

Re #38
Individuals vary. So what? That is why we include a great number of individuals when we sample populations: so that the indiviudal variation does not dominate the population signal. Usefulness of bcp as a temperature proxy and individual variability in the pattern of growth decline are two different issues that have been conflated here.

J. Peden: The other possible reason for the decrease in ring widths you observed would be precipitation. In fact, that is a very likely reason since water is most often the limiting factor to growth wherever lodgepole pine grows.

The reason bristlecones have been selected as temperature proxies is (aside from longevity) because in many sites growing season temperature and/or length are assumed to be the limiting factors to growth. The high elevation sites used have very short growing seasons and the warmth arrives long before the snow entirely dissapears.
The more I think about this, however, the more skeptical I am. Many of the places I have observed long-lived bristlecone pines one can find nearby mixed spruce/fir/bristlecone stands at nearly the same elevation. The only difference is aspect (and thus soil depth, snow loading and snowmelt). In these sites moisture is LESS limiting than the “classic bristlecone” sites nearby; but the trees are not useful as temperature proxies because they have crown and root competition – and because they don’t live all that long. The longevity of the oldest stands is because of avoidance of mortality agents – not because the trees are particurally resistant to disease, insects, or fire. Because the sites are harsh densities are too low for dwarf mistletoe to spread, sparse fuels (and a short fire window)remove the threat of wildfire, low temps. aand low densities both discourage beetle outbreaks, and the well-drained soils and narrow ring widths along with the open spacings make root disease uncommon. Other factors besides moisture limitations (notably wind and avalanche) help to maintain the wide spacings, but given the associated vegetation, aspect and topography of old bristlecone sites drought seems like it must be a factor.
Now there are a lot of bristlecone (and limber and whitebark) stands I have not seen, but I have looked at a lot of them, and often found individuals growing on better nearby sites, but they are not particurally old trees. This is just anecdotal evidence of course, but I believe it squares with the observations of foresters and biologists from the pre- anthropogenic global warming theory era.

The thing is – all this can be tested. You don’t have to simply guess which sites have a precipitation signal and which have a temperature signal. You could do controlled experiments (imagine that) and look at root/shoot ratios on different sites, stomatal density, cuticle thickness, or ideally by measuring water potential during the growing season. Some of these methods require destructive sampling so one might have to plant trees and wait a few years before beginning. All this would take time and $(plus some trained undergrads)but it seems better than just assuming given the stakes.